This invention relates to chucks for holding work pieces in lathes or like work piece rotating machines and particularly to means for rigidly holding the jaws against movement.
To carry out the present day precision in lathe work it is essential that the jaw faces which bear against the work accurately define a circle which is in absolute axial alignment with the axis of the work piece. This can be achieved by individually adjusting the jaws radially back and forth until the work is positively positioned in its intended location, but this is a very time consuming and tedious task. The working time which is lost in such a procedure is totally inconsistent with high productivity.
Various short cuts have been devised to shorten the setup time to accurately position the work piece and one of these ways is to provide the jaws with so-called soft material which can relatively easily be machined. This soft material makes it possible to rotate the chuck on the lathe in a normal manner and machine the soft material to absolutely accurate concentricity to receive the work. However, even this has its limitations as the slight slack which exists between the operating parts of the chuck mechanism results in a more or less malpositioning of the jaws.
The present invention provides means for firmly holding the jaws in fixed positions relative to the chuck body so that its faces which are to receive and grip the work can be machined to the size which will accommodate the workpiece. Then when the workpiece is placed between the jaws and the jaws are tightened against the work, the workpiece is accurately positioned axially and it can be machined with absolute precision.
The time required to bring the jaws to this accurate position is minute compared to the time required to individually adjust the jaws. Moreover, the use of the jaw locking means of this invention requires significantly less time and produces greater accuracy of positioning the jaw faces than the other means which have been devised. For example, the means of this invention is an improvement on the arrangement disclosed in U.S. Pat. No. 3,679,221 which issued to A. J. Behrens on July 25, 1972, to a much greater degree.
That patent shows an eccentric wheel 84 which is mounted on a transverse shaft 82 so that when the wheel is turned and wedged against the face of the chuck body the effect will be to wedge the jaw itself against motion. The structure of the patent has some utility but as the eccentric wheel has merely a camming action to hold the jaw in place, it is not fully satisfactory. The structure provided by the present invention is simple and inexpensive and serves to rigidly hold the jaws in position on the chuck body.
The invention can be applied to the jaws of the aforesaid patent to take the place of the wedge wheel and in order to show a representative application of the invention this description and drawings illustrate this use. This makes it unnecessary to illustrate the internal mechanisms of the chuck since the patent can be referred to for this disclosure. For this reason the structure and wording of the patent are hereby incorporated herein by this reference.
The patent shows a two piece jaw made up of a lower, master portion and a top portion but the invention may be applied to a jaw unit which is in one piece, i.e., the master and top portions are integral. The jaw to which the invention may be applied may therefore be a simple unit which has soft material at its work bearing face or the jaw may have the complexity of the mentioned patent. The internal jaw moving mechanism is also immaterial in the practice of this invention.